Display device

ABSTRACT

A display device includes a screen, first and second projectors, and a controller. The screen has first and second surfaces. The first projector projects a first horizontally non-inverted image as viewed from the first surface. The second projector projects a second horizontally non-inverted image as viewed from the second surface. The controller controls switching of an operation between the first and second projectors.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 fromJapanese Patent Application No. 2017-058358 filed Mar. 24, 2017.

BACKGROUND

(i) Technical Field

The present invention relates to a display device.

(ii) Related Art

Nowadays, collaboration is becoming more and more desirable regardlessof the types of jobs, and mediums and tools for connecting peoplenaturally and effectively are being demanded.

SUMMARY

According to an aspect of the invention, there is provided a displaydevice including a screen, first and second projectors, and acontroller. The screen has first and second surfaces. The firstprojector projects a first horizontally non-inverted image as viewedfrom the first surface. The second projector projects a secondhorizontally non-inverted image as viewed from the second surface. Thecontroller controls switching of an operation between the first andsecond projectors.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention will be described indetail based on the following figures, wherein:

FIGS. 1A and 1B are respectively a front view and a side view of adisplay device;

FIGS. 2A and 2B are schematic views for explaining switching of imageprojection by using two projectors;

FIGS. 3A and 3B are schematic views for explaining switching of imageprojection by using one projector;

FIGS. 4A and 4B are schematic views for explaining the detection ofpeople by using a sensor;

FIG. 5 is a schematic view for explaining the detection of people byusing a sensor;

FIG. 6 is a plan view for explaining detection distance zones;

FIGS. 7A and 7B are schematic views for explaining the projecting of thesame image on a screen;

FIGS. 8A and 8B are schematic views for explaining the projecting ofdifferent images on a screen;

FIGS. 9A and 9B are schematic views for explaining the projecting ofimages on a screen in accordance with the number of detected people;

FIGS. 10A and 10B are schematic views for explaining changing of thevisibility of a screen;

FIGS. 11A and 11B are schematic views for explaining changing of thevisibility of a screen;

FIG. 12 is a block diagram illustrating the configuration of a controlcircuit of the display device;

FIG. 13 is a flowchart illustrating an example of processing executed bya processor; and

FIG. 14 is a flowchart illustrating another example of processingexecuted by the processor.

DETAILED DESCRIPTION

An exemplary embodiment of the present invention will be described belowwith reference to the accompanying drawings.

Configuration

FIGS. 1A and 1B are respectively a front view and a side view of adisplay device 10 according to the exemplary embodiment.

The display device 10 includes a screen 12, a body 14, and a sensor 16.The display device 10 is movable as a result of being attached to legson casters, for example.

The screen 12 has a first surface 12 a and a second surface 12 b and isa so-called double-sided screen to display images on both of the firstand second surfaces 12 a and 12 b. If the first surface 12 a is a frontsurface and the second surface 12 b is a rear surface, images aredisplayed on both of the front and rear surfaces.

The body 14 supports the screen 12 so that the screen 12 can be fixed.The body 14 includes two projectors 20 and 22 and a processor 24. Theprocessor 24 controls the operations of the projectors 20 and 22.

The projector 20 is disposed in the upper side of the body 14 and on thebottom side of the first surface 12 a of the screen 12. The distancefrom the projector 20 to the screen 12 is determined by considering thefocal length of the projector 20. The projector 20 is a rear projectorand projects an image onto the screen 12.

The projector 22 is disposed in the upper side of the body 14 and on thebottom side of the second surface 12 b of the screen 12. The distancefrom the projector 22 to the screen 12 is also determined by consideringthe focal length of the projector 22. The projector 22, as well as theprojector 20, is a rear projector and projects an image onto the screen12.

The projectors 20 and 22 are formed as ultra-short focus projectors sothat the distance between the screen 12 and the projectors 20 and 22 canbe decreased, thereby reducing the size of the body 14.

The processor 24 controls the operations of the projectors 20 and 22 sothat the projectors 20 and 22 will project images on the first andsecond surfaces 12 a and 12 b. The processor 24 turns ON the projector20 so that an image can be projected on the screen 12 and be viewed fromthe second surface 12 b (rear projection). The processor 24 also turnsON the projector 22 so that an image can be projected on the screen 12and be viewed from the first surface 12 a (rear projection). When theprojector 20 is turned ON, a person on the side of the second surface 12b of the screen 12 views a horizontally non-inverted image. When theprojector 22 is turned ON, a person on the side of the first surface 12a of the screen 12 views a horizontally non-inverted image.

The processor 24 controls the switching of the ON/OFF operations betweenthe projectors 20 and 22 and turns ON the projectors 20 and 22 mutuallyexclusively. That is, at one timing, the processor 24 turns ON theprojector 20 so that a horizontally non-inverted image will be projectedas viewed from the second surface 12 b. At another timing, the processor24 turns ON the projector 22 so that a horizontally non-inverted imagewill be projected as viewed from the first surface 12 a.

The sensor 16 monitors a predetermined range of the first screen 12 aand that of the second screen 12 b so as to detect a person on the sideof the first surface 12 a and a person on the side of the second surface12 b. Upon detecting a person, the sensor 16 supplies a detection signalto the processor 24. By using a detection signal supplied from thesensor 16, the processor 24 controls the switching of the ON/OFFoperations between the projectors 20 and 22 and executes variousprocessing operations.

Although in this exemplary embodiment the projectors 20 and 22 are rearprojectors, they may be front projectors. In this case, the processor 24turns ON the projector 20 so that a person on the side of the firstsurface 12 a of the screen 12 can view a horizontally non-invertedimage, while the processor 24 turns ON the projector 22 so that a personon the side of the second surface 12 b of the screen 12 can view ahorizontally non-inverted image.

Although in this exemplary embodiment two projectors 20 and 22 areprovided, they may be combined into one projector. In this case, thesingle projector functions as a front projector at one timing andfunctions as a rear projector at another timing. For example, a singleprojector is disposed at a position at which the projector 20 isdisposed, that is, on the bottom side of the first surface 12 a of thescreen 12. At one timing, the processor 24 causes the projector tofunction as a front projector to project an image on the screen 12 sothat a person on the side of the first surface 12 a can view ahorizontally non-inverted image. At another timing, the processor 24causes the projector to function as a rear projector to project an imageon the screen 12 so that a person on the side of the second surface 12 bcan view a horizontally non-inverted image.

FIGS. 2A and 2B schematically illustrate the configuration of the screen12 of the display device 10 and also illustrate the display state ofimages on the first and second surfaces 12 a and 12 b.

The screen 12 includes a transparent substrate 121 made of glass or anacrylic material, for example. A diffusion coating 122 is formed on thetransparent substrate 121 on the side of the first surface 12 a, while adiffusion coating 123 is formed on the transparent substrate 121 on theside of the second surface 12 b. Instead of the diffusion coating 122, adiffusion film or a diffusion sheet may be attached to the transparentsubstrate 121 on the side of the first surface 12 a, while, instead ofthe diffusion coating 123, a diffusion film or a diffusion sheet may beattached to the transparent substrate 121 on the side of the secondsurface 12 b.

A polarizing film, a Fresnel lens, and a lenticular lens sheet are knownas a diffusion film or a diffusion sheet used for rear projection. Thescreen 12 in this exemplary embodiment is desirably a transparent screenwhich can be seen through, and thus, a diffusion film containing atransparent resin binder and light scattering particles having arefractive index different from the refractive index of the transparentresin binder may be used. As the transparent resin binder, a transparentresin containing at least one of acrylate, styrene, polycarbonate,polystyrene terephthalate, and acrylonitrile as a principal component,or a reactive resin such as an epoxy acrylate resin or a urethaneacrylate resin may be used. As the light scattering particles,crosslinked particles polymerized with monomers such as methacrylate andstyrene or crosslinked urethane particles may be used. Alternatively, adiffusion film including light transmitting portions and light diffusionportions which are alternately formed may be used.

The diffusion coating 122 diffuses an image projected by the projector20 and allows a person 200 on the side of the second surface 12 b of thescreen 12 to view a horizontally non-inverted image. For example, theprojector 20 projects an image “ABC”, and then, the person 200 on theside of the second surface 12 b can recognize “ABC” as a horizontallynon-inverted image, as shown in FIG. 2A.

The diffusion coating 123 diffuses an image projected by the projector22 and allows a person 300 on the side of the first surface 12 a of thescreen 12 to view a horizontally non-inverted image. For example, theprojector 22 projects an image “ABC”, and then, the person 300 on theside of the first surface 12 a can recognize “ABC” as a horizontallynon-inverted image, as shown in FIG. 2B.

The image display state when the screen 12 is a transparent screen willbe discussed. When the projector 20 is turned ON to project an image onthe diffusion coating 122, the person 200 on the side of the secondsurface 12 b views a horizontally non-inverted image, as shown in FIG.2A. In this state, if someone is present on the side of the firstsurface 12 a, this person sees a horizontally inverted image. Likewise,when the projector 22 is turned ON to project an image on the diffusioncoating 123, the person 300 on the side of the first surface 12 a viewsa horizontally non-inverted image, as shown in FIG. 2B. In this state,if someone is present on the side of the second surface 12 b, thisperson sees a horizontally inverted image. Accordingly, by using adetection signal from the sensor 16, the processor 24 controls theswitching of the ON/OFF operations between the projectors 20 and 22 inaccordance with various conditions. Examples of the conditions are theone concerning whether someone is present on the side of the firstsurface 12 a or the second surface 12 b of the screen 12 and the oneconcerning whether someone is present both on the sides of the first andsecond surfaces 12 a and 12 b.

FIGS. 3A and 3B illustrate a state in which the processor 24 controlsthe switching of the function of a single projector 21 between a rearprojector and a front projector. The projector 21 is disposed on theside of the first surface 12 a of the screen 12, for example.

At one timing, the processor 24 operates the projector 21 as a rearprojector to project an image on the diffusion coating 122 of the screen12 so that the person 200 on the side of the second surface 12 b canview a horizontally non-inverted image. For example, the projector 21projects an image “ABC”, and then, the person 200 on the side of thesecond surface 12 b of the screen 12 can recognize a horizontallynon-inverted image “ABC”, as shown in FIG. 3A.

At another timing, the processor 24 operates the projector 21 as a frontprojector to project an image on the diffusion coating 122 of the screen12 so that the person 300 on the side of the first surface 12 a can viewa horizontally non-inverted image. For example, the projector 21projects an image “ABC”, and then, the person 300 on the side of thefirst surface 12 a of the screen 12 can recognize a horizontallynon-inverted image “ABC”, as shown in FIG. 3B.

In FIGS. 3A and 3B, the projector 21 projects an image on the diffusioncoating 122 regardless of whether the projector 21 operates as a rearprojector or as a front projector. However, the projector 21 may projectan image on the diffusion coating 123 when it operates as a rearprojector and project an image on the diffusion coating 122 when itoperates as a front projector. Conversely, the projector 21 may projectan image on the diffusion coating 122 when it operates as a rearprojector and project an image on the diffusion coating 123 when itoperates as a front projector. Although in FIGS. 2A through 3B both ofthe diffusion coatings 122 and 123 are formed on the transparentsubstrate 121, at least one of the diffusion coatings 122 and 123 may beformed on or attached to the transparent substrate 121.

The display device 10 is a device which functions as a tool forconnecting people sharing the same interest. The display device 10 hasthe function of detecting people interested in certain information andthe function of enhancing smooth communication between people sharingthe same interest. The function of detecting people interested incertain information is achieved as a result of the sensor 16 detectingpeople viewing an image (information) displayed on the screen 12. Thefunction of enhancing smooth communication between people sharing thesame interest is achieved by changing the display mode of an imagedisplayed on the screen 12 in accordance with the detection result ofpeople. These functions will be discussed below.

Detection of People

FIGS. 4A and 4B schematically illustrate the detecting of people by thesensor 16. The sensor 16 includes a camera (first camera) which detectsa person on the side of the first surface 12 a of the screen 12 and acamera (second camera) which detects a person on the side of the secondsurface 12 b of the screen 12. The detection area of the first andsecond cameras is a range within a predetermined distance L0 from thescreen 12.

FIG. 4A illustrates the detecting of the person 200 on the side of thesecond surface 12 b of the screen 12 by the second camera when ahorizontally non-inverted image is being projected on the second surface12 b. The second camera detects that the person 200 is present withinthe predetermined distance L0 from the screen 12 and supplies adetection signal to the processor 24. By using the detection signal fromthe second camera, the processor 24 detects whether the person 200 isviewing the image projected on the screen 12 based on the face directionand the eye direction of the person 200, for example.

FIG. 4B illustrates the detecting of the person 300 on the side of thefirst surface 12 a of the screen 12 by the first camera when ahorizontally non-inverted image is being projected on the first surface12 a. The first camera detects that the person 300 is present within thepredetermined distance L0 from the screen 12 and supplies a detectionsignal to the processor 24. By using the detection signal from the firstcamera, the processor 24 detects whether the person 300 is viewing theimage projected on the screen 12 based on the face direction and the eyedirection of the person 300, for example.

In FIGS. 4A and 4B, the detection distance of the first camera and thatof the second camera are the same, that is, the predetermined distanceL0 is used. However, the detection distance of the first camera and thatof the second camera may be different. For example, if the first surface12 a is a front surface and the second surface 12 b is a rear surface,the detection distance of the first camera may be longer than that ofthe second camera. The predetermined distance L0 may not necessarily befixed and may be variable.

FIG. 5 schematically illustrates a state in which the detection distanceof the first and second cameras is variable. When the projector 20 isturned ON and a horizontally non-inverted image is being projected onthe second surface 12 b of the screen 12, if the person 200 is detectedby the second camera, the processor 24 changes the detection distance ofthe first camera from L0 to L1 (L0>L1). The reason for this is toexclude a person on the side of the first surface 12 a positionedfarther away from the screen 12 than the detected person 200 from thescreen 12. Likewise, when the projector 22 is turned ON and ahorizontally non-inverted image is being projected on the first surface12 a of the screen 12, if the person 300 is detected by the firstcamera, the processor 24 changes the detection distance of the secondcamera from L0 to L1 (L0>L1). When the detection distance is variable,the degree by which the detection distance of the first camera ischanged may be different from that of the second camera. Note that thedetection result of the first camera changes the detection distance ofthe second camera, and the detection result of the second camera changesthe detection distance of the first camera.

The processor 24 detects the presence of people by using the first andsecond cameras forming the sensor 16, and also estimates how much adetected person shows an interest in an image (information) projected onthe screen 12. This will hereinafter be called “the level of interest”.To estimate the level of interest of a detected person, the processor 24progressively changes what to look for in a detected person inaccordance with the distance between the detected person and the screen12.

FIG. 6 is a plan view of the display device 10 illustrating therelationship between the distance from a detected person to the screen12 and what to look for in the detected person. FIG. 6 shows thedetection area of the second camera on the side of the second surface 12b. However, the above-described relationship on the side of the firstsurface 12 a is similar to that shown in FIG. 6.

The processor 24 divides the detection distance (L0 or L1) into pluralzones according to the distance from the screen 12. For example, theprocessor 24 divides the detection distance into the following fourzones by using threshold distances R1, R2, and R3 (R1>R2>R3).

(1) First zone: the distance is R1 or greater

(2) Second zone: the distance is R2 or greater but smaller than R1

(3) Third zone: the distance is R3 or greater but smaller than R2

(4) Fourth zone: the distance is smaller than R3

When the second camera has detected the person 200 within the firstzone, the processor 24 determines whether the person 200 is still ormoving. If the person 200 is still, the processor 24 determines that theperson 200 is likely to view the screen 12 and judges that the person200 may be interested in an image on the screen 12. If the person 200 ismoving, the processor 24 determines that the person 200 is not likely toview the screen 12 and judges that the person 200 may not be interestedin the image on the screen 12. When the second camera has detected theperson 200 within the second zone, the processor 24 detects the facedirection of the person 200 and estimates the level of interest of theperson 200 in accordance with the face direction. Typically, if the facedirection of the person 200 faces the screen 12, the processor 24estimates the level of interest of the person 200 for the image(information) on the screen 12 at a relatively high level, and if theface direction of the person 200 does not face the screen 12, theprocessor 24 estimates the level of interest of the person 200 at arelatively low level. When the second camera has detected the person 200within the third zone, the processor 24 detects the eye direction of theperson 200 and estimates the level of interest of the person 200 inaccordance with the eye direction. Typically, if the detected eyedirection shows that the person 200 is looking at an image (information)on the screen 12, the processor 24 estimates the level of interest ofthe person 200 at a relatively high level. If the detected eye directionshows that the person 200 is not looking at an image (information) onthe screen 12, the processor 24 estimates the level of interest of theperson 200 at a relatively low level. When the second camera hasdetected the person 200 within the fourth zone, the processor 24 detectswhether the person 200 has showed some reaction for the image(information) displayed on the screen 12 and estimates the level ofinterest of the person 200 in accordance with the detection result.Typically, if the person 200 has showed some reaction, the processor 24estimates the level of interest of the person 200 for the image(information) at a relatively high level and changes the display stateof the image in accordance with the reaction. Examples of the reactionof the person 200 are making a specific gesture and saying something(voice). Alternatively, the second surface 12 b of the screen 12 may beformed as a touch panel, and the processor 24 may detect whether theperson 200 has touched the second surface 12 b of the screen 12.

While the projectors 20 and 22 are turned ON only mutually exclusively,the first and second cameras of the sensor 16 are constantly turned ONto detect the presence of people. For example, when the projector 20 isturned ON and a horizontally non-inverted image is being projected onthe second surface 12 b of the screen 12, the second camera detects theperson 200 on the side of the second surface 12 b, and, at the sametime, the first camera detects the person 300 on the side of the firstsurface 12 a. Likewise, when the projector 22 is turned ON and ahorizontally non-inverted image is being projected on the first surface12 a of the screen 12, the first camera detects the person 300 on theside of the first surface 12 a, and, at the same time, the second cameradetects the person 200 on the side of the second surface 12 b. Theprocessor 24 controls the switching of the ON/OFF operations between theprojectors 20 and 22 to change the display state of an image on thescreen 12 in accordance with the detection results of the persons 200and 300.

Changing of the image display state by the processor 24 will bediscussed below.

Changing of Image Display State

FIGS. 7A and 7B illustrate an example of image display control performedby the processor 24 in accordance with a detection result of the sensor16. The processor 24 first turns OFF the projector 20 and turns ON theprojector 22 to project a horizontally non-inverted image on the firstsurface 12 a of the screen 12. The image is “ABC”, for example.

When the person 300 on the side of the first surface 12 a of the screen12 views this image, the first camera of the sensor 16 detects theperson 300. If the person 300 is positioned within the first zone, theprocessor 24 determines whether the person 300 is still or moving. Ifthe person 300 is positioned within the second zone, the processor 24detects the face direction of the person 300. If the person 300 ispositioned within the third zone, the processor 24 detects the eyedirection of the person 300. If the person 300 is positioned within thefourth zone, the processor 24 determines whether the person 300 hasshowed some reaction for the image displayed on the screen 12.

When the first camera has detected the person 300 and when the secondcamera has not detected anyone, the processor 24 continues to turn ONthe projector 22 to project a horizontally non-inverted image on thefirst surface 12 a. Alternatively, even if the second camera does notdetect anyone, after the lapse of a predetermined time, the processor 24may turn ON the projector 20 and turn OFF the projector 22 to project ahorizontally non-inverted image on the second surface 12 b. In thiscase, the person 300 on the side of the first surface 12 a sees ahorizontally inverted image, as discussed above. Alternatively, theprocessor 24 may control the ON/OFF operations between the projectors 20and 22 in the following manner, for example, in accordance with the zonewithin which the person 300 is detected.

(a) When the Person 300 is Positioned within the First Zone

The processor 24 switches the ON/OFF operations between the projectors20 and 22 by using a time T1. More specifically, the processor 24 turnsON the projector 22 and turns OFF the projector 20 for a certain periodof the time T1, and turns OFF the projector 22 and turns ON theprojector 20 for the subsequent period of the time T1.

(b) When the Person 300 is Positioned within the Second Zone or theThird Zone

The processor 24 turns ON the projector 22 and turns OFF the projector20 for a period of a time T2 (T2>T1), and turns OFF the projector 22 andturns ON the projector 20 for the subsequent period of the time T1. Thatis, when the person 300 is positioned within the second zone or thethird zone, the period for which the projector 22 is ON is set to berelatively long so as to increase the time for the person 300 to view ahorizontally non-inverted image. The processor 24 may change the periodfor which the projector 22 is ON in accordance with the level ofinterest of the person 300 estimated in accordance with the facedirection of the person 300 in the second zone or the eye direction ofthe person 300 in the third zone. Typically, as the level of interest Iis higher, the period of time T for which the projector 22 is ON isincreased. More specifically, if the person 300 is positioned in thesecond zone and directs the face toward the screen 12, the processor 24sets the period for which the projector 22 is ON to be relatively longso as to increase the time for which the person 300 can view thehorizontally non-inverted image. If the person 300 is positioned in thesecond zone but does not direct the face toward the screen 12, theprocessor 24 sets the period for which the projector 22 is ON to berelatively short so as to decrease the time for which the person 300 canview the horizontally non-inverted image.

(c) When the Person 300 is Positioned within the Fourth Zone

Unless the second camera detects the person 200, the processor 24continues to turn ON the projector 22 and turn OFF the projector 20.This encourages the person 300 to show some reaction for the imagedisplayed on the screen 12. When the second camera has detected theperson 200, the processor 24 turns OFF the projector 22 and turns ON theprojector 20.

FIG. 7A illustrates a state in which the projector 22 is turned ON as aresult of the first camera detecting the person 300 and a horizontallynon-inverted image is being projected on the first surface 12 a of thescreen 12. FIG. 7B illustrates a state in which the projector 22 isturned OFF and the projector 20 is turned ON as a result of the secondcamera detecting the person 200 in the state shown in FIG. 7A, and ahorizontally non-inverted image is being projected on the second surface12 b of the screen 12. In FIG. 7B, the person 300 on the side of thefirst surface 12 a views the horizontally inverted image of the image“ABC”, that is, the image “ABC” viewed from the back side.

Upon detecting both of the persons 200 and 300, the processor 24switches the ON/OFF operations between the projectors 20 and 22 in thefollowing manner, for example, in accordance with the zones within whichthe persons 200 and 300 are positioned and the levels of interest of thepersons 200 and 300.

(d) When the Persons 200 and 300 are Positioned within the Same Zone

The processor 24 switches the ON/OFF operations between the projectors20 and 22 by using a time T3 (T3=T1 or T3<T1). More specifically, theprocessor 24 turns ON the projector 22 and turns OFF the projector 20for a period of the time T3, and turns OFF the projector 22 and turns ONthe projector 20 for the subsequent period of the time T3. Even when thepersons 200 and 300 are both positioned within the second zone or thethird zone, if the level of interest of the person 200 and that of theperson 300 are different, the processor 24 may switch the ON/OFFoperations between the projectors 20 and 22 in accordance with thelevels of interest of the persons 200 and 300. For example, if the levelof interest of the person 300 is higher than that of the person 200, theprocessor 24 may set the period for which the projector 22 is ON to belonger than that for which the projector 20 is ON.

If the persons 200 and 300 are both positioned within the fourth zone,the processor 24 switches the ON/OFF operations between the projectors20 and 22 in accordance with the reaction of the persons 200 and 300. Ifthe person 200 says “display on this side” or makes a gesture to turnover the screen 12, the processor 24 turns ON the projector 20 and turnsOFF the projector 22. If the person 300 touches the screen 12, theprocessor 24 turns ON the projector 22 and turns OFF the projector 20.

As discussed above, the screen 12 is a transparent screen which can beseen through, and a person on one side of the screen 12 can see an imageon the screen 12 and also see through the other side of the screen 12.That is, the person 300 can see an image displayed on one side of thescreen 12 and also see the person 200 on the other side of the screen12. Likewise, the person 200 can see an image on one side of the screen12 and also see the person 300 on the other side of the screen 12. Thisfacilitates communication between the persons 200 and 300 by means of animage on the screen 12 so as to connect the persons 200 and 300naturally.

(e) When the Persons 200 and 300 are Positioned within Different Zones

The processor 24 controls the ON/OFF periods of the projectors 20 and 22so that a horizontally non-inverted image can be projected for a longertime on the side on which the zone within which a person is positionedis closer to the screen 12. For example, when the person 200 ispositioned within the first zone and the person 300 is positioned withinthe second zone, the processor 24 sets the ON period of the projector 22to be relatively long and sets the ON period of the projector 20 to berelatively short. When the person 200 is positioned within the secondzone and the person 300 is positioned within the third zone, theprocessor 24 sets the ON period of the projector 22 to be relativelylong and sets the ON period of the projector 20 to be relatively short.The processor 24 may make further adjustment to the ON periods of theprojectors 20 and 22 in accordance with the levels of interest of thepersons 200 and 300. For example, when the person 200 is positionedwithin the first zone and the person 300 is positioned within the secondzone, the processor 24 basically sets the ON period of the projector 22to be relatively long and sets the ON period of the projector 20 to berelatively short. However, if the person 200 faces the screen 12 and thelevel of interest of the person 200 is found to be relatively high, theprocessor 24 may make further adjustment to increase the ON period ofthe projector 20.

When the persons 200 and 300 are positioned within different zones, aswell as they are positioned within the same zone, the person 300 can seean image displayed on one side of the screen 12 and also see the person200 on the other side of the screen 12. Likewise, the person 200 can seean image displayed on one side of the screen 12 and also see the person300 on the other side of the screen 12. This facilitates communicationbetween the persons 200 and 300 by means of an image on the screen 12 soas to connect the persons 200 and 300 naturally.

The processor 24 controls the switching of the ON/OFF operations betweenthe projectors 20 and 22 in accordance with the zone within which aperson is positioned and the level of interest of this person. However,the processor 24 may control the switching of the ON/OFF operationsbetween the projectors 20 and 22 only in accordance with the level ofinterest of a person regardless of the zone. More specifically, theprocessor 24 estimates the levels of interest of people by using atleast one of the face direction and the eye direction. The processor 24then switches the ON/OFF operations between the projectors 20 and 22 sothat a horizontally non-inverted image will be projected for arelatively long time for the person having a higher level of interest.If, instead of the projectors 20 and 22, the single projector 21 is usedand is disposed at the position of the projector 20, the processor 24controls the operation of the projector 21 in a similar manner. TurningON the projector 22 will be replaced by operating the projector 21 as afront projector, while turning ON the projector 20 will be replaced byoperating the projector 21 as a rear projector.

In FIGS. 7A and 7B, the projectors 20 and 22 project the same image“ABC” on the screen 12. The projectors 20 and 22 may project differentimages on the screen 12. For example, the projector 20 projects an image“ABC”, while the projector 22 projects an image “

”.

FIGS. 8A and 8B illustrate a state in which the projectors 20 and 22display different images. In FIG. 8A, at one timing, the processor 24turns ON the projector 20 to project an image “ABC” on the secondsurface 12 b of the screen 12. The person 200 on the side of the secondsurface 12 b views a horizontally non-inverted image “ABC”. At anothertiming, the processor 24 turns on the projector 22 to project an image “

” on the first surface 12 a of the screen 12. The person 300 on the sideof the first surface 12 a views a horizontally non-inverted image “

” If the image on the front side of a document is “ABC”, while the imageon the back side of the document is “

”, the person 200 views the image on the front side of the document,while the person 300 views the image on the back side of the samedocument.

Then, as shown in FIG. 8B, after the lapse of a predetermined time or inaccordance with the reaction (gesture, voice, or touch operation) of theperson 200 or 300, the processor 24 exchanges the image projected by theprojector 20 and that by the projector 22 for each other. That is, atone timing, the processor 24 turns ON the projector 20 to project theimage “

” on the second surface 12 b of the screen 12. The person 200 on theside of the second surface 12 b views a horizontally non-inverted image“

”. At another timing, the processor 24 turns ON the projector 22 toproject the image “ABC” on the first surface 12 a of the screen 12. Theperson 300 on the side of the first surface 12 a views a horizontallynon-inverted image “ABC”. The person 200 views the horizontallynon-inverted image “ABC” first and then sequentially views thehorizontally non-inverted image “

”, that is, the person 200 views the image on the front side first andthen sequentially views the image on the back side. The person 300 viewsthe horizontally non-inverted image “

” first and then sequentially views the horizontally non-inverted image“ABC”, that is, the person 300 views the image on the back side firstand then sequentially views the image on the front side. In short, thepersons 200 and 300 view the image on the front side and the image onthe back side of the same document alternately. This facilitatescommunication between the persons 200 and 300 by means of these images.

As described above, the processor 24 changes the display state of animage on the screen 12 by switching the ON/OFF operations between theprojectors 20 and 22 in accordance with whether someone is detected andthe level of interest of a detected person. The processor 24 may alsoswitch the ON/OFF operations between the projectors 20 and 22 inaccordance with the number of detected people. Changing of the imagedisplay state in accordance with the number of people by the processor24 will be discussed below.

Changing of Image Display State in Accordance with the Number of People

FIGS. 9A and 9B illustrate a state in which an image is displayed inaccordance with the number of detected people. In FIG. 9A, at onetiming, the processor 24 turns ON the projector 20 to project an image“ABC” on the second surface 12 b of the screen 12. The person 200 on theside of the second surface 12 b views a horizontally non-inverted image“ABC”. At another timing, the processor 24 turns ON the projector 22 toproject an image “

” on the first surface 12 a of the screen 12. The person 300 on the sideof the first surface 12 a views a horizontally non-inverted image “

”. If the image on the front side of a document is “ABC”, while theimage on the back side of the document is “

”, the person 200 views the image on the front side of the document,while the person 300 views the image on the back side of the samedocument.

After the lapse of a predetermined time, the processor 24 is supposed toexchange the image projected by the projector 20 and that by theprojector 22 for each other, as shown in FIG. 8B. That is, at onetiming, the processor 24 would turn ON the projector 20 to project theimage “

” on the second surface 12 b of the screen 12, and the person 200 on theside of the second surface 12 b would view a horizontally non-invertedimage “

”. At another timing, the processor 24 would turn ON the projector 22 toproject the image “ABC” on the first surface 12 a of the screen 12, andthe person 300 on the side of the first surface 12 a would view ahorizontally non-inverted image “ABC”. However, if the second camera ofthe sensor 16 detects two persons 200-1 and 200-2 on the side of thesecond surface 12 b of the screen 12, the processor 24 turns ON theprojector 22 to project the image “

” instead of the image “ABC” on the first surface 12 a of the screen 12.In this case, the person 300 continues to view the image “

”. In short, the processor 24 projects a horizontally non-inverted imagepreferentially on the side with more people over the side with fewerpeople. That is, the processor 24 displays the same image as that on theside with more people on the side with fewer people. As a result, theperson 300 views the same image as that viewed by the persons 200-1 and200-2, thereby promoting communication between the persons 200-1 and200-2 and the person 300.

As well as when the projectors 20 and 22 project different images, whenthey project the same image, the ON/OFF operations between theprojectors 20 and 22 may be switched in accordance with the number ofpeople. More specifically, if, as shown in FIG. 9B, more people arefound on the side of the second surface 12 b of the screen 12 than thaton the side of the first surface 12 a, the processor 24 may set theperiod for which the projector 20 is turned ON to be longer than thatfor which the projector 22 is turned ON.

Changing of Visibility

As discussed above, the screen 12 is a transparent screen which can beseen through. However, with the application of a voltage, the screen 12may be switched between the transparent or translucent state in which aperson is able to see through the other side of the screen and theopaque state in which a person is unable to see through the other sideof the screen. This can switch the visibility for a person on one sideof the screen 12 with respect to a person on the other side of thescreen 12, thereby promoting communication between people.

FIGS. 10A and 10B illustrate a state in which the visibility of thescreen 12 is changed. The processor 24 sets the screen 12 in the opaquestate as a default state so that the screen 12 is not seen through. Inthis state, as shown in FIG. 10A, the first camera of the sensor 16detects the person 300 on the side of the first surface 12 a of thescreen 12, and the processor 24 turns ON the projector 22 to project ahorizontally non-inverted image “ABC” on the first surface 12 a. Theperson 300 is able to see the horizontally non-inverted image “ABC”, butis unable to see through the other side of the screen 12, that is, thesecond surface 12 b of the screen 12, because the screen 12 is in theopaque state. In FIG. 10A, the opaque state of the screen 12 isindicated by hatching. Setting of the screen 12 in the opaque stateenhances the visibility of the image “ABC”.

Then, when the second camera of the sensor 16 has detected the person200 on the side of the second surface 12 b, the processor 24 changes thescreen 12 from the default opaque state to the transparent ortranslucent state, as shown in FIG. 10B. This enables the person 300 tosee the image and also to see the person 200 on the other side of thescreen 12, thereby enhancing smooth communication with the person 200.

Instead of simply changing the screen 12 between the two states, thatis, the opaque state and the transparent or translucent state, theprocessor 24 may progressively or sequentially change the screen 12 inorder of the opaque state, the translucent state, and the transparentstate, or may change the screen 12 in this order in accordance with thezone within which the person 200 is positioned or the level of interestof the person 200. For example, when the person 200 is positioned withinthe first zone, the processor 24 maintains the screen 12 to be in theopaque state, and when the person 200 sequentially approaches the secondzone and the third zone in this order, the processor 24 sequentiallyincreases the transparency of the screen 12. When the person 200 reachesthe fourth zone, the processor 24 makes the screen 12 completelytransparent. In another example, when the person 200 is positionedwithin the third zone, if the person 200 does not look at the screen 12and the level of interest of the person 200 is thus considered to berelatively low, the processor 24 sets the screen 12 in the translucentstate. If the person 200 looks at the screen 12 and the level ofinterest of the person 200 is thus considered to be relatively high, theprocessor 24 sets the screen 12 in the transparent state. Bysequentially increasing the transparency of the screen 12 in accordancewith the interest of a person on the other side of the screen 12,communication with the person can be enhanced if this person seems to beinterested in an image (information) displayed on the screen 12 andcommunication with the person can be avoided if this person does notshow much interest in the image (information).

FIGS. 11A and 11B illustrate another mode of a state in which thevisibility is changed. The screen 12 is set in the transparent state asa default state, and, as shown in FIG. 11A, the processor 24 turns ONthe projector 22 to project predetermined images on the almost entiresurface of the screen 12.

Then, when the second camera of the sensor 16 has detected the person200 on the side of the second surface 12 b of the screen 12, theprocessor 24 projects the predetermined images on the lower portion ofthe screen 12, as shown in FIG. 11B, so as to enable the person 300 toeasily see the person 200 on the side of the second surface 12 b withoutbeing blocked by the images. Instead of changing the position of theimages, the entirety or part of the images may be erased to improve thevisibility. In this manner, changing of the position or the content ofan image to be projected on the screen 12 enhances the visibility,thereby facilitating communication between people. The processor 24 maychange the visibility by sequentially changing the position or thecontent of an image to be projected on the screen 12 in accordance withthe zone within which the person 200 is positioned or the level ofinterest of the person 200.

As described above, the processor 24 controls the switching of theON/OFF operations between the projectors 20 and 22 (or switching of thefunction of the projector 21 between a front projector and a rearprojector) in accordance with a detection signal received from thesensor 16. This control processing may be implemented by softwareprocessing in accordance with a processing program stored in a programmemory, such as a read only memory (ROM), by using a random accessmemory (RAM) as a working memory. At least part of the processing may beexecuted by hardware processing by using a circuit, such as anapplication specific integrated circuit (ASIC) or a field programmablegate array (FPGA).

FIG. 12 is a block diagram illustrating the configuration of a controlcircuit including the processor 24 that executes display controlprocessing of the display device 10.

A microcomputer 32 is loaded within the body 14 of the display device10. The microcomputer 32 includes a ROM 26, a RAM 28, and aninput-output interface 30, as well as the processor 24. The processor24, the ROM 26, the RAM 28, and the input-output interface 30 areconnected to one another via a communication bus. The microcomputer 32may also include a hard disk drive (HDD) or a solid state drive (SDD)which stores image data, and may be connected to a communication networkvia a communication interface.

The processor 24 reads a processing program stored in the ROM 26 andexecutes it by using the RAM 28 as a working memory, thereby executingthe above-described processing operations. Operations executed by theprocessor 24 will be explained more specifically. The processor 24outputs a control command and image data to be projected on the screen12 to the projectors 20 and 22 via the input-output interface 30 so asto control the ON/OFF operations of the projectors 20 and 22. Theprocessor 24 receives detection signals (camera image signals) from afirst camera 161 and a second camera 162 forming the sensor 16 via theinput-output interface 30. The processor 24 then processes the detectionsignals so as to detect a person and estimate the level of interest ofthe detected person by using the face direction or the eye direction ofthe detected person. If a detected person is positioned within thefourth zone and makes a gesture, outputs voice, or performs a touchoperation, the processor 24 also receives information concerning such agesture, voice, or touch operation via the input-output interface 30.The time parameters used for switching the ON/OFF operations between theprojectors 20 and 22 by using a predetermined time and the distanceparameters used for dividing the detection distance into plural zonesare stored in the ROM 26 as part of the processing program. Image datato be projected by the projectors 20 and 22 is stored in an externalmemory, such as an HDD or an SDD, as discussed above. Such image datamay alternatively be supplied from an external server via acommunication network.

Processing executed by the processor 24 includes the ON/OFF switchingoperation between the projectors 20 and 22 (or thefront-projection/rear-projection switching operation of the projector21), the detection operation of people, the determining operation ofzones, the estimating operation of the level of interest, and so on.These operations may be executed by plural processors in a distributedmanner instead of being executed by a single processor.

FIG. 13 is a flowchart illustrating an example of processing executed asa result of the processor 24 reading the processing program.

In step S101, when the display device 10 is powered ON to start theindividual elements, the processor 24 determines whether the firstcamera 161 has detected someone on the side of the first surface 12 a ofthe screen 12 and whether the second camera 162 has detected someone onthe side of the second surface 12 b of the screen 12. More specifically,the processor 24 receives image data obtained by the first camera 161and that by the second camera 162 so as to extract images of people fromthe image data. To extract image of people, template matching processingor processing using neural network models obtained by learning may beused.

If nobody has been detected neither on the first surface 12 a nor thesecond surface 12 b (NO in step S101), the processor 24 sets a switchingtime Ta and a switching time Tb in step S102. When the predeterminedtime is T1, the processor 24 sets the switching times Ta and Tb to beTa=Tb=T1. The switching time Ta is a time for which the projector 20 isON and the projector 22 is OFF. The switching time Tb is a time forwhich the projector 20 is OFF and the projector 22 is ON.

After setting the switching times Ta and Tb in step S102, the processor24 turns ON the projector 20 and turns OFF the projector 22 in stepS106. Turning ON the projector 20 can project a horizontallynon-inverted image on the second surface 12 b.

Then, the processor 24 determines in step S107 whether the switchingtime Ta has elapsed after turning ON the projector 20. If the switchingtime Ta has not elapsed (NO in step S107), the processor 24 continues toturn ON the projector 20.

If the switching time Ta has elapsed (YES in step S107), the processor24 turns OFF the projector 20 and turns ON the projector 22 in stepS108. Turning ON the projector 22 can project a horizontallynon-inverted image on the first surface 12 a.

Then, the processor 24 determines in step S109 whether the switchingtime Tb has elapsed after turning ON the projector 22. If the switchingtime Tb has not elapsed (NO in step S109), the processor 24 continues toturn ON the projector 22. If the switching time Tb has elapsed (YES instep S109), the processor 24 returns to step S101 and repeats steps S101through S109. With this operation, if nobody is detected, the projectors20 and 22 are alternately turned ON based on the same switching timeTa=Tb=T1 so that a horizontally non-inverted image will be repeatedlyprojected on the second surface 12 b and the first surface 12 aalternately.

If someone is detected on the side of at least one of the first andsecond surfaces 12 a and 12 b (YES in step S101), the processor 24determines the zone within which the detected person is positioned instep S103. The processor 24 estimates the level of interest of thedetected person in step S104. The processor 24 may determine the zone bymeasuring the distance R from the screen 12 to the detected person andthen by comparing the distance R with the preset distance thresholds R1,R2, and R3 (see FIG. 6). The processor 24 may estimate the level ofinterest of the detected person in accordance with whether the detectedperson is still (first zone), whether the face direction of the detectedperson faces the screen 12 (second zone), whether the eye direction ofthe detected person directs toward the screen 12 (third zone), andwhether the detected person 12 has showed some reaction for the screen12 (fourth zone). If the levels of interest of people detected withinthe first through fourth zone are set to be:

-   -   within first zone: I1    -   within second zone: I2    -   within third zone: I3    -   within fourth zone: I4,        the levels of interests are typically estimated at I1<I2<I3<I4.        If the level of interest of a person being still within the        first zone is I1s, while that of a person moving within the        first zone is I1m, the levels of interests are estimated at        I1m<I1s. If the level of interest of a person facing the screen        12 within the second zone is I2s, while that of a person who        does not face the screen 12 within the second zone is I2m, the        levels of interests are estimated at I2m<I2s. If the level of        interest of a person looking at the screen 12 within the third        zone is I3s, while that of a person who does not look at the        screen 12 within the third zone is I3m, the levels of interests        are estimated at I3m<I3s. If the level of interest of a person        showing some reaction for the screen 12 within the fourth zone        is I4s, while that of a person who does not show any reaction        for the screen 12 within the fourth zone is I4m, the levels of        interests are estimated at I4m<I4s.

After determining the zone in step S103 and estimating the level ofinterest in step S104, the processor 24 sets the switching times Ta andTb by using at least one of the zone and the level of interest in stepS105. Setting of the switching times Ta and Tb may be performed by usinga predetermined function having at least one of the zone and the levelof interest as a dependent variable.

Alternatively, a table which defines the association between at leastone of the zone and the level of interest and the switching times Ta andTb may be used. The function or the table is also stored in the ROM 26as part of the processing program. It is now assumed that the switchingtimes Ta and Tb are set by using the table which defines theabove-described association. If the first camera 161 has detected theperson 300 within the first zone and if the second camera 162 has notdetected anyone, the switching times Ta and Tb are set to be Ta=Tb=T1.If the first camera 161 has detected the person 300 within the secondzone and the second camera 162 has detected the person 200 within thesecond zone and if the level of interest of the person 300 is higherthan that of the person 200, the switching times Ta and Tb are set to beTa<Tb. If the first camera 161 has detected the person 300 within thefourth zone and if the second camera 162 has detected the person 200within the third zone, the switching times Ta and Tb are set to beTa<<Tb. Setting of Ta<Tb means that the time for which the projector 22is ON is longer than that for which the projector 20 is ON and thusmeans that a horizontally non-inverted image viewed by a person having ahigher level of interest will be projected for a longer time. Setting ofthe switching times Ta and Tb is not restricted to these examples, andthose who skilled in the art are capable of setting the switching timesTa and Tb by using at least one of the zone and the level of interest.The level of interest of a detected person may be estimated by includingthe position (zone) of this person, and then, the switching times Ta andTb may be set by using the estimated level of interest.

After setting the switching times Ta and Tb in step S105, the processor24 turns ON the projector 20 and turns OFF the projector 22 in stepS106. Turning ON the projector 20 can project a horizontallynon-inverted image on the second surface 12 b.

Then, the processor 24 determines in step S107 whether the switchingtime Ta has elapsed after turning ON the projector 20. If the switchingtime Ta has not elapsed (NO in step S107), the processor 24 continues toturn ON the projector 20.

If the switching time Ta has elapsed (YES in step S107), the processor24 turns OFF the projector 20 and turns ON the projector 22 in stepS108. Turning ON the projector 22 can project a horizontallynon-inverted image on the first surface 12 a.

Then, the processor 24 determines in step S109 whether the switchingtime Tb has elapsed after turning ON the projector 22. If the switchingtime Tb has not elapsed (NO in step S109), the processor 24 continues toturn ON the projector 22. If the switching time Tb has elapsed (YES instep S109), the processor 24 returns to step S101 and repeats steps S101through S109.

The processing will be described specifically by way of example.

It is now assumed that the person 300 is positioned within the secondzone and the person 200 is also positioned within the second zone andthat the level of interest of the person 300 and that of the person 200are the same. The processor 24 thus sets the switching times Ta and Tbto be Ta=Tb. The period for which the projector 20 is ON and that forwhich the projector 22 is ON are equal to each other, and horizontallynon-inverted images are alternately projected on the first surface 12 aand the second surface 12 b of the screen 12. For example, when thefront side and the back side of a document are alternately projected bythe projectors 20 and 22, a horizontally non-inverted image on the frontside is projected by the projector 20→a horizontally non-inverted imageon the back side is projected by the projector 22→a horizontallynon-inverted image on the back side is projected by the projector 20→ahorizontally non-inverted image on the front side is projected by theprojector 22→ . . . . The person 300 thus views a horizontallynon-inverted image of the front side and that of the back side in orderof the front side→back side→front side→back side→ . . . . It appears tothe person 300 as if the document were rotating around the center axisin the vertical direction. It also appears to the person 200 as if thedocument were rotating.

In this state, if the person 300 approaches the screen 12 up to thethird zone and gazes at the screen 12, the processor 24 detects the eyedirection of the person 300 and estimates the level of interest of theperson 300 at a high level. The processor 24 then considerably increasesthe switching time Tb and sets it to be Ta<<Tb. As a result, the periodfor which the projector 22 is turned ON, that is, the period for whichthe person 300 is seeing the horizontally non-inverted image,considerably increases. It thus appears to the person 300 as if therotating document were temporarily stopped. The person 300 is thus ableto see the content of the document in greater details.

In this state, if the person 200 also approaches the screen 12 up to thethird zone and gazes at the screen 12, the processor 24 estimates thelevel of interest of the person 300 and that of the person 200, and ifthe processor 24 determines that the level of interest of the person 300and that of the person 200 are the same, it resets the switching timesTa and Tb to be Ta=Tb. Then, it again appears to the persons 300 and 200as if the document were rotating around the central axis in the verticaldirection. If the person 300 then approaches the screen 12 up to thefourth zone and gives an instruction by saying or making a gesture“stop” or touching the screen 12, the processor 24 sets the switchingtimes Ta and Tb to be Ta<<Tb again. It thus appears to the person 300 asif the rotating document were temporarily stopped.

The exemplary embodiment has been discussed above. However, theinvention is not restricted to this exemplary embodiment, and variousmodifications may be made. Some modified examples will be describedbelow.

First Modified Example

In the above-described exemplary embodiment, the display device 10includes the screen 12 and one projector 21 or two projectors 20 and 22.The screen 12 may be constituted by a liquid crystal display. In thiscase, the liquid crystal display is desirably formed as a transparentliquid crystal display so that a person can see through the other sideof the display. If the liquid crystal display is not a transparentliquid crystal display, it may still look like a pseudo-transparentdisplay by attaching opaque liquid crystal displays to each other and bysuperposing background images captured by cameras on the opposite sides.

Second Modified Example

In the above-described exemplary embodiment, the position, facedirection, eye direction, and reaction of a detected person are used forestimating the level of interest of this person. In addition to thesefactors, the time for which a detected person has been staying near thescreen 12 may also be used for estimating the level of interest of thedetected person. As the time for which a detected person has beenstaying is longer, the processor 24 may estimate the level of interestat a higher level.

Third Modified Example

In the above-described exemplary embodiment, when the plural persons200-1 and 200-2 are detected on the side of the second surface 12 b ofthe screen 12, as shown in FIG. 9B, the level of interest of each of thepersons 200-1 and 200-2 is estimated. However, as the representativelevel of interest of plural persons on the side of the first surface 12a or the second surface 12 b, the total level of interest of the pluralpersons may be calculated or the highest level of interest among thelevels of interest of the individual persons may be calculated.

Fourth Modified Example

In the above-described exemplary embodiment, as shown in FIG. 13, thelevel of interest of a detected person is estimated by using theposition, face direction, eye direction, and reaction of the detectedperson. More simply, without estimating the level of interest, theON/OFF operations between the projectors 20 and 22 may be switcheddirectly in accordance with the position, face direction, eye direction,and reaction of a detected person. In this configuration, although thelevel of interest is not clearly indicated, it is indirectly reflectedin the switching operations of the projectors 20 and 22 by means of theposition, face direction, eye direction, and reaction of the detectedperson.

FIG. 14 is a flowchart illustrating processing executed by the processor24 in this configuration.

The processor 24 determines in step S201 whether the first camera 161has detected someone on the side of the first surface 12 a and whetherthe second camera 162 has detected someone on the side of the secondsurface 12 b by using detection signals (image signals) from the firstand second cameras 161 and 162.

If nobody has been detected (NO in step S201), in step S204, theprocessor 24 sets a default image display mode, which is used whennobody has been found, concerning whether an image will be rotated orstopped. For example, an image is rotated for a certain period of time,or an image is displayed only on the first surface 12 a and is fixedthere. Then, in step S205, the processor 24 turns ON and OFF theprojectors 20 and 22 so that the image display mode set in step S204 canbe performed. If the processor 24 has set the image display mode so thatthe image would be rotated, it alternately turns ON and OFF theprojectors 20 and 22 at regular intervals. If the processor 24 has setthe image display mode so that the image would be stopped (fixed), theprocessor 24 only keeps turning ON the projector 22, for example.

If someone has been detected (YES in step S201), the processor 24determines the zone within which the detected person is positioned instep S202, and detects the face direction, eye direction, and reactionof the detected person in step S203. Then, in step S204, the processor24 refers to a table stored in a memory, which defines the associationbetween the image display mode (rotate or stop) and the zone, facedirection, eye direction, reaction so as to set the image display mode.Then, in step S205, the processor 24 turns ON and OFF the projectors 20and 22 so that the image display mode set in step S204 can be performed.More specifically, if the person 300 is detected within the first zoneon the side of the first surface 12 a and if the person 300 faces thescreen 12, the processor 24 sets the image display mode so that theimage will be stopped, and only keeps turning ON the projector 22 tokeep displaying a horizontally non-inverted image on the first surface12 a. If the person 300 is detected within the first zone on the side ofthe first surface 12 a and the person 200 is also detected within thefirst zone on the side of the second surface 12 b, and if both of thepersons 200 and 300 are facing the screen 12, the processor 24 sets theimage display mode so that the images will rotate and alternately turnsON and OFF the projectors 20 and 22.

As the above-described table stored in a memory, a first table for acase in which a person is detected on the side of one of the first andsecond surfaces 12 a and 12 b and a second table for a case in which aperson is detected on the sides of both of the first and second surfaces12 a and 12 b may be used.

In the flowchart of FIG. 14, the processor 24 may set the image displaymode (rotate or stop) in accordance with at least one of the position,face direction, eye direction of a detected person, and the time forwhich this person has been staying near the screen 12. Those who skilledin the art are capable of changing the image display mode by combiningthese factors in a desired manner. Changing of the image display modemay be controlled by switching the ON/OFF operations between theprojectors 20 and 22 and by switching the projecting of horizontallynon-inverted images by the projectors 20 and 22. The ON/OFF operationsbetween the projectors 20 and 22 may be switched by varying the dutyratio of the period for which the projector 20 is ON to that for whichthe projector 22 is ON.

Fifth Modified Example

In the above-described exemplary embodiment, the image display state ischanged also in accordance with the reaction of a detected person. Inthis case, in accordance with a specific reaction of a detected person,part of an image may be enlarged or reduced or be rotated. For example,when the projector 20 is turned ON to display an image “ABC” for theperson 200, if the person 200 gestures to spread the palm of a hand orto spread the fingers apart, the processor 24 may detect such a gestureand enlarge the image “ABC”. If the person 200 gestures to turn thewrist, the processor 24 may detect such a gesture and rotate the image.Instead of projecting a single image, plural images may be projected, asshown in FIGS. 11A and 11B. The plural images may be rotated together,and in accordance with a specific reaction or the eye direction of theperson 200, the processor 24 may stop rotating the images.

Sixth Modified Example

In the above-described exemplary embodiment, the time for which adetected person has been staying near the screen 12 is detected. In thiscase, the time for which a detected person has been staying or viewingthe screen 12 may be measured, and if such a time reaches a certaintime, the display device 10 may offer an incentive to this person via acertain medium. For example, if an image displayed on the screen 12concerns an advertisement, a coupon related to this advertisement may beissued to this person.

Seventh Modified Example

In the above-described exemplary embodiment, the processor 24 may rotatean image when detecting a person. In this case, sound, light, or abreeze may be output from the display device 10 together with therotation of the image.

The foregoing description of the exemplary embodiment of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Obviously, many modificationsand variations will be apparent to practitioners skilled in the art. Theembodiment was chosen and described in order to best explain theprinciples of the invention and its practical applications, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with the various modifications as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the following claims and their equivalents.

What is claimed is:
 1. A display device comprising: a screen havingfirst and second surfaces; a first projector that projects a firsthorizontally non-inverted image as viewed from the first surface; asecond projector that projects a second horizontally non-inverted imageas viewed from the second surface; and a controller that estimates alevel of interest of a person based on a signal from a sensor, andcontrols switching of an operation between the first and secondprojectors based on the estimated level of interest of the personsatisfying a criterion.
 2. The display device according to claim 1,wherein the first and second projectors are rear projectors.
 3. Thedisplay device according to claim 2, wherein, at one timing, thecontroller turns ON the first projector and turns OFF the secondprojector so as to project the first horizontally non-inverted image onthe first surface, and at another timing, the controller turns OFF thefirst projector and turns ON the second projector so as to project thesecond horizontally non-inverted image on the second surface.
 4. Thedisplay device according to claim 1, wherein: the first and secondprojectors form a single projector including a front projecting functionand a rear projecting function; and the controller controls switching ofan operation between the front projecting function and the rearprojecting function.
 5. The display device according to claim 4,wherein, at one timing, the controller turns ON the front projectingfunction and turns OFF the rear projecting function so as to project thefirst horizontally non-inverted image on the first surface, and atanother timing, the controller turns OFF the front projecting functionand turns ON the rear projecting function so as to project the secondhorizontally non-inverted image on the second surface.
 6. The displaydevice according to claim 1, wherein the first and second projectorsproject an identical image as the first and second horizontallynon-inverted images.
 7. The display device according to claim 1, whereinthe first and second projectors project different images as the firstand second horizontally non-inverted images.
 8. The display deviceaccording to claim 1, wherein the screen is a transparent screen whichis seen through.
 9. The display device according to claim 1, wherein thescreen is switchable between a state in which the screen is seen throughand a state in which the screen is not seen through.
 10. The displaydevice according to claim 1, wherein the level of interest is estimatedbased on a determination of a distance between the person and thesensor.
 11. The display device according to claim 1, wherein obtainingthe estimated level of interest comprises determining a zone in whichthe person is detected, among a plurality of zones.
 12. The displaydevice according to claim 11, wherein a duration of projection by thefirst projector and the second projector is determined based on the zonein which the person is detected.
 13. The display device according toclaim 1, wherein the level of interest is estimated based on adetermination of a direction of the face of the person detected by thesensor.
 14. The display device according to claim 1, wherein the levelof interest is estimated based on a determination of a direction of theeyes of the person detected by the sensor.
 15. The display deviceaccording to claim 11, wherein a duration of projection by the firstprojector and the second projector is determined based on a number ofpeople detected by the sensor.
 16. A display device comprising: aprojector configured to display a first image on a first surface ascreen and a second image on a second surface of the screen; acontroller configured to estimate a level of interest of a person basedon a signal from a sensor; and control the projector to display thefirst image and the second image based on the estimated level ofinterest of the person satisfying a criterion.
 17. The display deviceaccording to claim 16, wherein the level of interest is estimated basedon a determination of a distance between the person and the sensor. 18.The display device according to claim 16, wherein obtaining theestimated the level of interest comprises determining a zone in whichthe person is detected, among a plurality of zones.
 19. The displaydevice according to claim 16, wherein the level of interest is estimatedbased on a determination of a direction of the face of the persondetected by the sensor.
 20. The display device according to claim 16,wherein the level of interest is estimated based on a determination of adirection of the eyes of the person detected by the sensor.